Experience Gained from 400 Injection Well KOH Clay Stabilization Treatments
NORMAN, CHUCK, TIORCO Inc.
Water injection in clay sensitive sandstone formations often results in decreased permeability and low injectivity. Some types of clays, including montmorillonites, swell upon contact with fresh water. Migrating clays, including kaolinites and illites, reduce permeability as they become trapped in pore throat openings.
KOH clay stabilization results from the interaction of caustic with the clay in the presence of potassium ions. The KOH-clay chemical reaction permanently alters the clay chemistry so that the clay minerals are unaffected by changes in water composition. Several field case histories, discussed in the following paragraphs, demonstrate that KOH can mitigate the effects of both swelling and migrating clays. Field results indicate that a single KOH treatment is effective over the economic life of the well.
Laboratory studies and empirical results indicate that the most important considerations for optimizing KOH treatment results are: (1) KOH concentration; (2) KOH contact time with reservoir rock; (3) maintaining a constant flowrate of the KOH solution during treatment, and; (4) reservoir temperature.
The majority of KOH treatments have been applied in Cretaceous sandstone formations in the Powder River Basin of Wyoming. However KOH offers the potential for injectivity improvement in other clay sensitive formations, and should be considered as an alternative to hydraulic fracturing in some areas. The process is potentially valuable to operators in California, who encounter clay problems in certain formations.
Finally, a simple waterflood simulation is presented in order to evaluate the economics of KOH.
AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California